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[Author] Atsushi SASAKI(6hit)

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  • A Time- and Communication-Optimal Distributed Sorting Algorithm in a Line Network and Its Extension to the Dynamic Sorting Problem

    Atsushi SASAKI  

     
    PAPER-Algorithms and Data Structures

      Vol:
    E87-A No:2
      Page(s):
    444-453

    This paper presents a strictly time- and communication-optimal distributed sorting algorithm in a line network. A strictly time-optimal distributed sorting algorithm in a line network has already been designed. However, its communication complexity is not strictly optimal and it seems to be difficult to extend it to other problems, such as that related to multiple elements in a process, and also the dynamic sorting problem where the number of elements each process should have as its solution is not the same as that in the initial state. Therefore, the algorithm in this paper was designed by an alternative approach to make it strictly time- and communication-optimal. Moreover, an extension to the dynamic sorting problem is described.

  • A New Blind Adaptive Array Antenna Based on CMA Criteria for M-Ary/SS Signals Suitable for Software Defined Radio Architecture

    Miho KOZUMA  Atsushi SASAKI  Yukihiro KAMIYA  Takeo FUJII  Kenta UMEBAYASHI  Yasuo SUZUKI  

     
    PAPER

      Vol:
    E91-A No:8
      Page(s):
    1982-1989

    M-ary/SS is a version of Direct Sequence/Spread Spectrum (DS/SS) aiming to improve the spectral efficiency employing orthogonal codes. However, due to the auto-correlation property of the orthogonal codes, it is impossible to detect the symbol timing by observing correlator outputs. Therefore, conventionally, a preamble has been inserted in M-ary/SS signals. In this paper, we propose a new blind adaptive array antenna for M-ary/SS systems that combines signals over the space axis without any preambles. It is surely an innovative approach for M-ary/SS. The performance is investigated through computer simulations.

  • A Distributed Task Assignment Algorithm with the FCFS Policy in a Logical Ring

    Atsushi SASAKI  

     
    PAPER-Algorithms and Data Structures

      Vol:
    E88-A No:6
      Page(s):
    1573-1582

    This paper presents a distributed task assignment algorithm in a logical unidirectional ring, which guarantees that almost all tasks are assigned to servers with the first come first served (FCFS) policy without a global clock. A task assignment for a process is obtained in the time period needed for a message to circle the ring. This time period is almost optimal for a unidirectional ring. The FCFS policy is very important in terms of task fairness and can also avoid starvation and provide an efficient response time. Simulation results show that the algorithm generally works better than conventional task assignment or load balancing schemes with respect to both mean response time and task fairness.

  • Formulation of Mobile Agent Allocation and Its Strong NP-Completeness

    Atsushi SASAKI  Tadashi ARARAGI  Shigeru MASUYAMA  Keizo MIYATA  

     
    LETTER-Complexity Theory

      Vol:
    E88-D No:5
      Page(s):
    1060-1063

    We formally define the mobile agent allocation problem from a system-wide viewpoint and then prove that it is strongly NP-complete even if each agent communicates only with two agents. This is the first formal definition for scheduling mobile agents from the viewpoint of load balancing, which enables us to discuss its properties on a rigorous basis. The problem is recognized as preemptive scheduling with independent tasks that require mutual communication. The result implies that almost all subproblems of mobile agent allocation, which require mutual communication of agents, are strongly NP-complete.

  • Design of 1 m2 Order Plasma Excitation Single-Layer Slotted Waveguide Array with Conducting Baffles and Quartz Glass Strips Using the GSM-MoM Analysis

    Takuichi HIRANO  Kimio SAKURAI  Jiro HIROKAWA  Makoto ANDO  Tetsuya IDE  Atsushi SASAKI  Kazufumi AZUMA  Yukihiko NAKATA  

     
    PAPER-Antennas and Propagation

      Vol:
    E89-B No:5
      Page(s):
    1627-1635

    The authors have proposed a 1 m2 single-layer slotted waveguide array consisting of conducting baffles and quartz glass strips positioned in front of the slot aperture, which is referred to as a vacuum window, for microwave plasma excitation. The effect of the complicated outer vacuum window hinders the realization of uniform distribution. In this paper, a unit-cell of the alternating-phase fed single-layer slotted waveguide array with the vacuum window is analyzed by generalized scattering matrix method (GSM)-method of moments (MoM) hybridization analysis, and the array is designed to realize uniform aperture electromagnetic field distribution, where the plasma and the chamber is neglected. The GSM-MoM analysis gives reliable numerical results while the MoM has numerical errors due to singularities of Green's function for a long cavity. Uniform aperture EM field distribution outside of the vacuum window is observed in near field measurements using a 1/5 scale model antenna, and the validity of the analysis and design is verified.

  • A Time-Optimal Distributed Arrangement Selection Algorithm in a Line Network

    Atsushi SASAKI  

     
    PAPER-Parallel/Distributed Algorithms

      Vol:
    E86-D No:2
      Page(s):
    228-237

    This paper defines the distributed arrangement selection problem in a line network in a distributed context and describes the design of a strictly-time-optimal algorithm which solves the problem with a limited local memory space. The problem is regarded as a combined distributed sorting and k-selection problem, namely a problem of sorting elements that are not larger than the kth minimum element in predetermined processes. The algorithm also provides a solution to a resource allocation problem in a line network in a strictly-optimal time.